Top Speed Calc with Load

Lightweight / Folding / Portable EVs - seats optional
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kentsfreeman   100 mW

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Top Speed Calc with Load

Post by kentsfreeman » Mar 22 2015 5:04pm

Guys,

Finally got my first build done and out on the road today.

Runs smoothly however top speed is lower than what I thought.

Using 6s setup with NTM 270KV motor. Gearing is 15 - 44 and using 83mm wheels. So based on my calculations theoretical top speed is 19.6mph however I am only hitting 12mph to 14mph.

I weigh about 205 pounds. Roads are mostly flat with slight uphill but only hitting 14.6mph on slight downhill and 11-12mph on flat to slight uphill.

Just wanted to make sure that is within range based on the load the motor is trying to push.

Thanks!

torqueboards   100 MW

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Re: Top Speed Calc with Load

Post by torqueboards » Mar 22 2015 5:31pm

I think your running a 16:44. Gearing is setup for high torque which is why your speed is lower. Are you on 6S, can't remember?

I have 36T coming soon which should fix the gearing issue. The drive wheel should be lower in teeth for a higher top speed.

If anyone does know the calculation with load. I can create a calculator for it. My calculations pretty much came out to the same as yours which is definitely wrong too.
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kentsfreeman   100 mW

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Re: Top Speed Calc with Load

Post by kentsfreeman » Mar 22 2015 6:13pm

Yes running 6s. Might have counted the teeth wrong on the drive pulley so ya, probably 16:44.

brent   1 W

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Re: Top Speed Calc with Load

Post by brent » Mar 22 2015 9:46pm

Image
If your mechanical setup is 100% efficient and there's no rolling resistance, your speed will creep upwards to approach the point on the graph above when (the radius of your wheel) x (force from air resistance) is equal to (your motor's torque) * (1 / your gearing ratio).

A legitimate top speed calculation is difficult, especially since the companies that make the outrunners we use don't provide a lot of technical specs. You can fudge a calculation by taking your free speed and multiplying it by ~80%, though. I think that'd explain your 15mph top speed.

chuttney1   100 W

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Re: Top Speed Calc with Load

Post by chuttney1 » Mar 22 2015 10:03pm

A theoretical speed of 19.6 mph and actual speed of 12 to 14 mph. Some power losses are to be taken into account, though this is useful data. I wish more people on this forum could do more load and no load testing to help create a better speed calculator.

kentsfreeman   100 mW

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Re: Top Speed Calc with Load

Post by kentsfreeman » Mar 23 2015 3:20pm

I recalibrated my esc to my transmitter and noticed higher rpm on the motor. Will report back with new top speed once I can get it out on the road, but it seems like my esc just needed to be recalibrated.

saming   10 W

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Re: Top Speed Calc with Load

Post by saming » Mar 23 2015 4:04pm

I might be very light or something but with this calculator program im right on my top speed if not slow by 1 mph.
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kentsfreeman   100 mW

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Joined: Mar 06 2015 11:01pm

Re: Top Speed Calc with Load

Post by kentsfreeman » Mar 23 2015 5:26pm

So seems it was just an issue with the ESC. Recalibrated it and hit 18mph.

torqueboards   100 MW

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Re: Top Speed Calc with Load

Post by torqueboards » Mar 23 2015 5:34pm

kentsfreeman wrote:So seems it was just an issue with the ESC. Recalibrated it and hit 18mph.
Perfect. I totally forgot about that. Did you set your ESC to Very High for timing and acceleration? Those are my current settings and it runs perfectly fine and doesn't get that hot at all.

I could of sworn my calculations were spot on too. Wondering how you got that 14mph but totally slipped my mind.
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kentsfreeman   100 mW

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Re: Top Speed Calc with Load

Post by kentsfreeman » Mar 23 2015 6:54pm

Yes it is set to very high timing. Probably going to turn that down as the way it is geared that is way to much acceleration, lol.

Also getting some cogging issues when going full throttle even when I am already moving at a decent speed.

Really have to be gentle on the throttle with the current setup.

Might just be the low gearing ratio though.

torqueboards   100 MW

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Re: Top Speed Calc with Load

Post by torqueboards » Mar 23 2015 7:00pm

16/44 gearing, right?

What kind of clogging issues at full throttle? I may know what your talking about but not sure maybe if you describe it more I might.
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kentsfreeman   100 mW

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Re: Top Speed Calc with Load

Post by kentsfreeman » Mar 23 2015 7:12pm

So if I give it to much throttle from low speed or a stop (while I am on the board) the motor instead of spinning smoothly becomes very jumpy and makes a chugging type sound. It fills like it is shaking while on the board but I am assuming the ESC is sending the wrong voltage because they are not communicating.

Today I was at about half throttle going 10mph or so and went to full throttle and it cogged up and I had to jump of the board it it is sort of like throwing on the brakes as the motor stops spinning smoothly.

torqueboards   100 MW

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Re: Top Speed Calc with Load

Post by torqueboards » Mar 23 2015 8:47pm

I would try adding a ferrite ring to your ESC signal wire if you don't already have one. That can sometimes fix that stuttering/cogging effect IMO. Organize the signal wire and the RC receiver to get more signal if it can by making it more open from the enclosure and/or away from other wires. Sometimes a capacitor bank helps too.

Sorry to ask but if you can remind me what ESC, Motor, Receiver - you are using.
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kentsfreeman   100 mW

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Joined: Mar 06 2015 11:01pm

Re: Top Speed Calc with Load

Post by kentsfreeman » Mar 23 2015 9:47pm

I am running the Hobbyking 150a ESC with NTM 270kv motor and Hobbyking GT2B transmitter and receiver.

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